The present invention relates to an implement for orientating a tool at a predetermined angle with respect to a target surface to be engaged by the tool. The invention is particularly useful in surgical tools for harvesting and implanting bone plugs to repair damaged bone tissue, and is therefore described below with respect to such an application, but it will be appreciated the invention can be used in other applications. The invention also relates to a method of harvesting and implanting bone plugs to repair damaged bone tissue.
The surfaces of the bones in a sinovial joint, such as the knee, have protective covers made up of articular cartilage. The cartilage optimizes weight distribution over the joint surface, minimizes friction and wear, and allows for a smooth glide over the joint surface with motion. Beneath this protective cover of articular cartilage lies a layer of subchondral bone, followed by cancellous bone.
A defect in, or damage to, the cartilage will cause local irritation, producing pain and swelling. In patients with a disease known as osteochondritis dissecans (OCD), there is a localized full osteocartilaginous separation at the level of the subchondral bone that can damage the protective cover. Unless the lesion repairs itself or is treated, the disease will progress. OCD lesions may occur in any joint, but they occur most often in the knee and the ankle.
The treatment of all cartilage lesions depends on the patient's age and the extent of the lesion. Treatment options for patients first manifesting symptoms of such lesions may include non-surgical treatment or surgical treatment. Young people usually respond well to non-surgical treatment. However, adults generally require at least diagnostic arthroscopy to evaluate the lesion, and frequently also surgical intervention to treat it. Surgical procedures to treat the lesions include open or arthroscopic drilling, debridement, reduction and fixation with pins or screws, bone grafting, chondrocyte implantation and osteochondral grafts.
Surgical techniques for autologous osteochondral grafting involve transplanting bone plugs. This typically involves removing the damaged bone tissue by drilling or cutting a hole at the site of the damage (the recipient site), and filling this hole with a bone plug with its cartilage layer as harvested or extracted from healthy tissue in non-load-bearing joint surfaces in the patient's body (the donor site).
Surgical instruments are currently available which may be used to harvest or extract a bone plug from a donor site and then to implant it into a pre-formed hole at the recipient site. A conventional harvesting instrument typically includes a tube having a cutting edge at the distal end. To extract a plug, the tube is driven into the bone at the donor site and then removed, taking with it a plug of healthy bone tissue. The plug is then generally transferred to a delivery device for implantation at the receiving site. Examples of methods and devices for harvesting and implanting bone plugs are described in U.S. Pat. Nos. 6,767,354, 6,395,011, 6,306,142, 6,017,348, 5,919,196 and 5,782,835.
The success of grafting (implanting) depends on, among other factors, the fit in size and shape of the harvested graft (bone plug) to the hole formed at the receiving site. Perpendicularity of the harvesting and of the drilling operations is essential in order to achieve a good fit between the layers of the graft and of the receiving site.
Several devices and systems are currently in use for performing osteochondral grafting. However, they generally do not include means to establish perpendicularity of the harvested plug, but rather rely on visual estimation only. In procedures performed arthroscopically, the narrow field of vision makes visual assessment difficult and not sufficiently accurate for this purpose.
Another drawback of most available devices and systems is that they require the transfer from the harvester into a separate delivery device, or require the application of a delivery sheath over the harvester tube (e.g., see for example the above-cited U.S. Pat. No. 6,767,354). Transferring the graft from one tube to another presents a serious hazard to graft integrity as it can lead to the separation of the cartilage layer from the bone plug. Transferring the graft from the harvester tube via a delivery sheath, as in U.S. Pat. No. 6,767,354, is generally done by mallet blows on the proximal face of the plug, and therefore also involves a grave hazard of separation of the cartilage from the bone because of the friction between the plug and the wall of the delivery sheath.
It will appreciated that while the invention is particularly useful in surgical operations for harvesting bone plugs, the invention may also be used in many other applications, for example in drilling holes through workpieces at a precise predetermined angle to the workpiece surface, particularly where the viewing of the workpiece surface is obstructed or limited.